1. Field of the Invention
The invention relates to an apparatus for controlling signal-transmission power, a mobile station including the apparatus for controlling signal-transmission power, a method of controlling signal-transmission power, and a program for carrying out the method, and more particularly to such an apparatus, such a mobile station, such a method, and such a program all for controlling maximum signal-transmission power among power for transmitting a plurality of signals multiplexed with one another.
2. Description of the Related Art
In a field of communication of a mobile such as a mobile phone, 3GPP (3rd Generation Partnership Project) defines and suggests a standard for W-CDMA (Wideband-Code Division Multiple Access). Furthermore, as a method of transferring data at a high rate in an up-link channel, that is, from a user equipment UE to a base station, HSUPA (High Speed Uplink Packet Access) is additionally defined.
FIG. 16 is a block diagram illustrating a structure of a related HSUPA signal-transmission system.
As illustrated in FIG. 16, the related HSUPA signal-transmission system comprises a diffuser 101, a FIR filter 103, a DAC (Digital to Analog converter) 104, and a signal-transmission RF (Radio Frequency) part 105.
As illustrated in FIG. 16, in the HSUPA signal-transmission system, E-DPDCH (Enhanced Dedicated Physical Data Channel) is input into the diffuser 101 as a channel for transferring data therethrough, and E-DPCCH (Enhanced Dedicated Physical Control Channel) is input into the diffuser 101 as a channel for transferring control data therethrough.
These E-DPDCH and E-DPCCH are additionally code-multiplexed with a related W-CDMA Uplink channel, accomplishing high-rate data communication (non-patent reference 1).
As illustrated in FIG. 16, four or less code-multiplexing (E-DPDCH4, E-DPDCH3, E-DPDCH2, E-DPDCH1) is defined with respect to E-DPDCH (non-patent reference 2).
Furthermore, HS-DPCCH (High Speed Dedicated Physical Control Channel) used for HSDPA (High Speed Downlink Packet Access) is input into the diffuser 101 as a channel for transferring information about data re-transmission. HS-DPCCH is additionally code-multiplexed with a related W-CDMA Uplink channel.
If a number of channels to be code-multiplexed with W-CDMA channel were increased as mentioned above, PAR (Peak to Average power Ratio) defined as a ratio between peak power and average power in transmission of a signal would be increased, resulting in that power amplifier PA is deformed, and thus, ACLR (Adjacent Channel Leakage power Ratio) is deteriorated.
In 3GPP, there is defined a specification in which a number of channels to be multiplexed in a signal-transmission circuit equipped in a user equipment UE, and maximum signal-transmission power is fixedly reduced, if HSUPA (High Speed Uplink Packet Access) is not used (not-patent reference 3).
As a reduction (a back-off) of the maximum signal-transmission power, three fixed constants are stored in a lookup table in accordance only with a gain factor (βc/βd).    Non-patent reference 1: 3GPP Release 6 TS 25.211 V6.7.0, 5.2.1.3    Non-patent reference 2: 3GPP Release 6 TS 25.213 V6.4.0, 4.2    Non-patent reference 3: 3GPP Release 5 TS 25.101 V5.d.0, 6.2.2
On the other hand, if HSUPA (High Speed Uplink Packet Access) is used, a number of channels to be multiplexed is further increased, resulting in millions of a possible combination of gain factors β. Thus, if a lookup table were used in order to determine a reduction in maximum signal-transmission power in a related process, it would be difficult to carry out simply grouping with the result of an increase in an error in a reduction in maximum signal-transmission power.
In order to accurately calculate a reduction in maximum signal-transmission power, it would be necessary to sample waveforms of signals for a certain period of time in a path downstream of the FIR (Finite Impulse Response) filter 103, and process the results of sampling. However, it takes a lot of burden to process the results of sampling, and accordingly, a circuit structure is complex and a circuit size is increased in order to accomplish processing the results of sampling immediately prior to transmission of a signal.
If a reduction in maximum signal-transmission power were small relative to a peak, ACLR (Adjacent Channel Leakage power Ratio) would be deteriorated, and, in contrast, if a reduction in maximum signal-transmission power were wastefully high relative to a peak, there would be caused a problem that a cell area covered by a base station is narrowed.
Thus, there is a need for a method of accurately and readily calculating an optimal reduction in maximum signal-transmission power.